The dynamics of phytoplankton biomass in the vertically mixed south-eastern part of the Bisan Strait, in the Seto Inland Sea of Japan, may be considered to be strongly dependent not only on nutrients but also on light status. This was investigated by examining variations in chlorophyll-a (Chl-a), nutrients, and Secchi-disc depth through high-frequency sampling (a mean of once every 1.7 days) at the same station from April to October 2019. Precipitation during the Japanese rainy season (East Asian monsoon rains) was associated with a decrease in salinity from 32 to 31 in late July. The highest concentration of dissolved inorganic nitrogen (DIN), the most deficient nutrient, also was recorded in late July in association with seasonal precipitation. However, the measured Chl-a peak (max. 4 μg l−1) in early August was not as high as expected, possibly due to low water clarity. A relatively small but substantial peak of DIN (max. 4 μM) was recorded in mid-August, which coincided with the passing of a typhoon. The small peak of DIN coupled with higher water clarity thereafter was followed by a phytoplankton bloom from mid-August to early September, at which the highest Chl-a (7 μg l−1) occurred. It is suggested that increased light penetration enhanced the efficiency of nutrient assimilation and thereby triggered the late-summer phytoplankton bloom. In contrast to the adjacent stratified areas, light rather than nutrient status appears to be the key determinant for the onset of phytoplankton blooms in the Bisan Strait.

中文翻译：

---

日本浊流碧山海峡光照状态对浮游植物生物量的重要性：高频采样研究结果

在日本濑户内海的 Bisan 海峡东南部垂直混合的浮游植物生物量的动态可能被认为不仅强烈依赖于营养物质，而且还强烈依赖于光照状态。这是通过检查叶绿素的变化来研究的-一种（氯-一种)、养分和 Secchi-disc 深度通过高频采样（平均每 1.7 天一次）在同一站点于 2019 年 4 月至 10 月进行。日本雨季（东亚季风雨）期间的降水量与减少有关7 月下旬，盐度从 32 到 31。溶解无机氮 (DIN) 的最高浓度是最缺乏的营养物质，也记录在 7 月下旬与季节性降水有关。然而，测得的 Chl-一种峰值（最大 4 μg l-1) 8 月初没有预期的那么高，可能是由于水的透明度低。8 月中旬记录到一个相对较小但相当大的 DIN 峰值（最大 4 μM），这与台风的经过相吻合。此后 DIN 的小峰值加上更高的水清澈度，随后是 8 月中旬至 9 月初的浮游植物水华，此时最高的 Chl-一种（7微克升-1） 发生了。有人认为，增加的光穿透提高了养分同化的效率，从而引发了夏末浮游植物的大量繁殖。与相邻的分层区域相比，光而不是营养状况似乎是碧山海峡浮游植物水华爆发的关键决定因素。